Sorry just realised I didn't explain myself enough,
I want to run 2 SME servers. One as a front end and one as a back end email server.
Users would check email on the front email server via Outlook or Webmail, the real email would be held on the back end email server.
I would like to do this so that users don't ever get any real access to the mailserver which holds the email. The only access is through the front end mailserver.